Charge ordering in low dimensional organic conductors: Structural aspects

The paper points out the importance of the coupling between anions and donors in order to achieve the 4kF charge localization observed in (TMTTF)2PF6, δ‐(EDT‐TTF‐CONMe2)2Br and (o‐DMTTF)2Cl/Br salts, the 2kF charge density wave (CDW) ground state of α‐(BEDT‐TTF)2KHg(SCN)4 and the metal to insulator transition of α‐(BEDT‐TTF)2I3. This coupling leads to a cooperative displacement wave of the anions accompanied by a modulation of the density of π holes on the donors. We distinguish two principal anion–donor coupling mechanisms: a direct mechanism via the Hartree anion potential on donor sites and an indirect mechanism via the polarization of σ bonds activated by the modification of the H bonds network. Both kinds of interaction are tuned by the relative displacement of the anions with respect to the donors.